Is HTML case sensitive?
In an example I'm working with it says:
<!DOCTYPE html>
Would <!doctype html> or <!DocType Html> work differently (or not at all)?
Asked
Active
Viewed 7.9k times
51
Peter Mortensen
- 30,738
- 21
- 105
- 131
David Oneill
- 12,502
- 16
- 58
- 70
6 Answers
61
No, but it's considered good practice to keep HTML markup lowercase.
Peter Mortensen
- 30,738
- 21
- 105
- 131
Roddick
- 757
- 6
- 7
-
45Incomplete. Tag names and attribute names are case-insensitive, while attribute values are case-sensitive. – powerboy Oct 03 '11 at 23:10
-
22That's because the names are part of the spec. Values are whatever the user wants them to be. – Matt Hughes Nov 11 '13 at 16:45
-
4@MattHughes, yes, but the attribute value case sensitivity is surely part of the spec, no? – Bruce Pierson Aug 11 '18 at 19:42
25
From http://www.w3.org/TR/html5/syntax.html
In other words,
<!DOCTYPE html>, case-insensitively.Many strings in the HTML syntax (e.g. the names of elements and their attributes) are case-insensitive, but only for characters in the ranges U+0041 to U+005A (LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and U+0061 to U+007A (LATIN SMALL LETTER A to LATIN SMALL LETTER Z). For convenience, in this section this is just referred to as "case-insensitive".
Community
- 1
- 1
Kenny Dorman
- 381
- 2
- 5
-
Nevertheless it is not a bad idea to write `DOCTYPE` upper-cased to be backward compatible to XML. – Matthias Dieter Wallnöfer Jan 11 '20 at 18:03
16
In addition to the other answers given, if you set the header Content-type: application/xhtml+xml, your browser will throw and XHML error if you don't type DOCTYPE in uppercase and html in lowercase:
<!DOCTYPE html>
Using the XHTML content type isn’t recommended because the page won't be rendered in some browsers (e.g. IE8 and below), but it's certainly interesting to know.
Liam Newmarch
- 3,935
- 3
- 32
- 46
7
Generally, HTML is case-insensitive, but there are a few exceptions. Entity names (the things that follow ampersands) are case-senstive, but many browsers will accept many of them entirely in uppercase or entirely in lowercase; a few must be cased in particular ways. For example, Ç is Ç and ç is ç. Other combinations of upper and lower case are no good.
supercat
- 77,689
- 9
- 166
- 211
